I agree for some of those, but it's more than this. First of all, a longer duration lets you pre-SW without wasting too much of it. You want it for Heroic Beth'tilac. 2 of the 3 transitions as I'm going up the web, I Shield Wall before getting to the boss, wasting maybe 1-2 seconds, but it's there for quite some time and smooths the damage. No amount of offset 6 ilvl rating increase will outscale a 6 second extra 50% DR that works on bleed and magical. There's more than Alysrazor's ground phase, enraged Hatchlings plus a tick or two from the Lava Spew, etc. Then Heroic Rhyolith has some pretty insane tank damage, a 18 second SW is wanted here, magic damage on top of that, plus in the phase 2 burn, as the whole raid is getting destroyed, you want it there too.
Originally Posted by Pyrea
I'm not overestimating the 4p t11, but we shouldn't be overestimating the 2p t12 when threat is a non-issue, and a 6 ilvl stat upgrade if you talk about offpieces. To me, the 4p t11 is more valuable.